The present invention relates to sheet-outfeed units of printing machines, in which the printed sheets are transported from a last printing station to a sheet stack. More particularly, the invention pertains to a pick-up unit, a number of which are arranged on the movable loop chain of the sheet-outfeed unit at equal intervals.
Pick-up units disclosed in DDR patent application No. WPB 41f/240 356 are each provided with a streamline-shaped cover in which the front portion, as viewed in the direction of transporting of the printed sheets, has a cross-section formed as a cut drop. A plate is arranged at the end of the pick-up unit, on which plate counter gripping members are mounted. The disadvantage of this construction of the pick-up unit is that, since the unit is totally covered, the disassembling and reassembling of the grippers become difficult.
Furthermore, the front edge of the printed sheet, while it is passing the region of the dryer, is partially covered by the above mentioned cover whereby the printed sheet in this region can not be completely dried. A non-uniform drying of the sheet unfavorably affects the quality of the printed sheet because some ink remaining at the front edge of the sheet causes the blurring.
A further disadvantage of the known structure of the pick-up unit is that the mounting of the counter gripping members on the plate is expensive because each counter gripping member must be individually adjusted and then additionally rigidly secured to the plate.
A tensile strength of the known sheet-pick-up unit in the plane of the counter gripping members is insignificant because the cover is interrupted in the region where the grippers and counter gripping elements lie opposite each other.
The pick-up unit, which is disclosed in the German patent publication DE-OS No. 21 40 442, is provided with the cover which encircles the gripper shaft, for increasing the moment of resistance. The disadvantage of this construction of the sheet-pick-up unit is that a pair composed of a gripper and a counter gripping member operates centrally in the pick-up unit whereby the transported sheet lies on the portion of the cover. Therefore a pressure and counter pressure of the printed sheets can cause the transferring of the ink onto the cover.
A further disadvantage of the known construction is that a shadow freedom is not warranted during the application of the dryer to the printed sheet and the sheet is therefore not uniformly dried.